Internal aircraft fuel tanks sometimes develop leaks which are usually detected either by observing fuel dripping from the cavity drain of the fuel tank and/or during manufacturing when the fuel tank fails an internal pressure decay test. Once a leak has been detected, the leak must be isolated and located, which is normally a rather timely and costly process.
To pinpoint a leak in an internal fuel tank, an exemplary process includes first isolating the fuel tank from the fuel system by removing the plumbing and capping the fittings and connections within the fuel tank. This alone can be a rather timely operation as some existing fuel cells have well over one hundred fittings to which internal caps must be added. After the fuel tank has been isolated accordingly, air pressure is introduced into the fuel tank itself, usually at about four pounds per square inch (4.0 psig), and the source providing the air pressure is turned off. The pressure within the fuel tank is monitored over a period of time, for example, on a test cart gage to check for pressure decay. If the pressure decay rate is higher than that which is allowed by the applicable process specifications, the fuel tank leaks and thus will not hold fuel. Eventually, fuel will leak from the external cavity drain of the fuel tank.
In an attempt to locate an origin of a detected leak, various methods can be employed including incremental refueling and defueling of the fuel tank, and inspection of randomly selected seals in an attempt to identify a possible O-ring leak in any one of the numerous fittings. Each of these processes can require an extensive amount of time without any guarantee that the origin of the detected leak will be found. Indeed, it is not uncommon that the leak's origin will not be found in which case the fuel tank will have to be removed and replaced. Removing and replacing a fuel tank, however, can also be a rather timely and costly process.